This invention relates to an image synthesizer and more particularly to an image synthesizer of an image editing apparatus for editing, creating and displaying a new pictorial image by processing two or more sets of image data.
When an image editor of this type is used to synthesize a new image from two or more original source images, the conventional procedure has been to operate its keyboard, while watching the superposedmutually transparent display of these source images, to adjust the two-dimensional positional relationships among them. In connection with such a procedure, one method of superposingly synthesizing two mutually transparent images A and B, for example, is to read out pixel values of these images A and B respectively stored in different image memories M.sub.a and M.sub.b by means of a data processor to calculate their average values and to display such average values calculated individually for each pixel. Another method is to read out pixel values, for example, of the image A stored in a display memory M.sub.v and those of the image B stored in an image memory M.sub.b by a data processor to calculate their average values and to display such average values after rewriting the display memory M.sub.v by these calculated average values.
With either of these exemplary methods, data processing becomes extremely time-consuming because averages of two or more sets of image data must be calculated for all pixels in the superposed area. In the case of a composite image requiring no transparency in superposition, the averaging process is carried out only for pixels in boundary areas between different images to make the boundary lines less conspicuous but the amount of calculations to be carried out is still significantly large. By the second of the two methods described above, furthermore, there is the disadvantage of losing one of the source images because its image data stored in the display memory is replaced by the newly calculated average values. In order to make this image restorable, its data must be temporarily saved and this means that an increased memory capacity is required.